A method and a display device with pixel repartition optimization

ABSTRACT

A method for presenting an image on a display device ( 100 ) includes modifying the image by applying a geometric transformation to the image so that an area of the image on the display device is presented to a viewer with higher density of pixels than that in the rest of the image (S 18 ).

TECHNICAL FIELD

The present disclosure generally relates to a display device with pixelrepartition optimization. The display device may be a user wearabledisplay device such as a head mounted display (HMD) device, but not belimited to such kind of display device.

BACKGROUND ART

These HMD devices are mainly composed of a display module (LCD or OLED,for example), and an optics. This optics is usually designed to modifythe light as if it was generated at infinity or at finite but largedistance (e.g. human eye hyper-focal distance) from the viewer (to allowthe accommodation to a screen placed so close), and to increase thefield of view to improve the sentiment of immersion.

These HMD devices may be coupled with a sensor such as inertialmeasurement unit (IMU) to measure the position of a user's head. Thanksto the sensor, the video content provided to the user through thedisplay can depend on his/her head orientation, thus the user can movein a virtual world and feel a sentiment of immersion.

US 2012/0154277 A1 discloses to track user's head and eye position inorder to determine a focal region for the user and to couple a portionof the optimized image to the user's focal region. However, any conceptsfor optimizing pixel repartition of an image to be presented on thedisplay are not considered in US 2012/0154277 A1.

SUMMARY

According to one aspect of the present disclosure, a method forpresenting an image on a display device is provided. The method includesmodifying the image by applying a geometric transformation to the imageso that an area of the image on the display device is presented to aviewer with higher density of pixels than that in the rest of the image.

According to another aspect of the present disclosure, a display devicefor presenting an image comprising a processor is provided. Theprocessor is configured to modify the image by applying a geometrictransformation to the image so that an area of the image on the displaydevice is presented to a viewer with higher density of pixels than thatin the rest of the image.

The object and advantages of the present disclosure will be realized andattained by means of the elements and combinations particularly pointedout in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the presentdisclosure will become apparent from the following description inconnection with the accompanying drawings in which:

FIG. 1 represents the visual acuity depending on the angular positionaround the fovea;

FIG. 2 presents the general overview according an embodiment of thepresent disclosure;

FIG. 3 represents a distortion applied by an optical element;

FIG. 4 illustrates a geometric transformation process applied to animage according to the embodiment of the present disclosure;

FIG. 5 illustrates a design of a lens with the same functionality thanin the original system;

FIG. 6 shows the whole optical system of the HMD device of the presentembodiment;

FIG. 7 shows a perceived field of view plotted as a function of thefield position on the display;

FIG. 8 schematically illustrates a display device according to anembodiment of the present disclosure, in which FIG. 8(a) is a plan viewof the device and FIG. 8(b) is a front view of the device;

FIG. 9 is a block diagram illustrating components of the control moduleshown in FIG. 8; and

FIG. 10 is a flow chart illustrating an example of a process performedby the display device according to an embodiment of the presentdisclosure.

DESCRIPTION OF EMBODIMENTS

In the following description, various aspects of an exemplary embodimentof the present disclosure will be described. For the purpose ofexplanation, specific configurations and details are set forth in orderto provide a thorough understanding. However, it will also be apparentto one skilled in the art that the present disclosure may be implementedwithout the specific details present herein.

In order to facilitate the understanding of the concept of an embodimentof the disclosure, some characteristics of the Human Visual System arefirst introduced.

FIG. 1 represents the visual acuity depending on the angular positionaround the fovea, which is cited from the page related to the “foveacentralis” of the Wikipedia. The fovea is the central area of the eyewhere the density of cones is the highest. This area represents only acouple of degrees, where the visual acuity is maximal. This acuitydecreases rapidly when the field of view increases (see FIG. 1). Itmeans that, even if a large field of view is required to bring a feelingof immersion to the viewer, the details cannot be perceived by theperipheral vision.

The resolution of the display devices, generating images thanks toseparated discrete pixels, is based on this visual acuitycharacteristic: depending on the distance of observation, the pixelscannot be perceived if their spatial frequency is higher than theseparation capability of the eye.

The Human eye, in the fovea area, can approximately discriminate twopoints separated by one minute of arc angle. It means for instance thata 42″ HD (High Definition) screen 1920×1080 pixels, having a width of 93cm, can be watched at a distance of 166 cm, to have a pixel density of60 pixels per degree in its central part, corresponding approximately tothe visual acuity.

Here, an example will be discussed in relation to an exemplary HMDdevice having a resolution of 1280×800 pixels. In this example, thehorizontal field of view will be approximately 90° (or 110° depending onthe sources), and the theoretical number of pixels per eye will be 640(but likely closer to 500 practically): 500 pixels distributed over 90°implies a pixel density lower than 5 pixels per degree. That is 10 timeslower than what should be required to respect Nyquist-Shannon samplingtheorem for a visual acuity of one arc minute. Even if the nextgeneration of this HMD should be based on a display having 1920×1080pixels, the resolution should remain far below the visual acuity in thefovea area.

Inversely, the pixel density in the peripheral vision area is too highto be perceived by the human eye as visual acuity decreases strongly inthe visual periphery.

This disclosure illustratively describes a display device such as HMDdevice increasing the pixel density in an area of the display, anddecreasing this density in the peripheral areas of the area withincreased pixel density. Since the eyes can move in the content providedby the display, this increase of density is not limited to the extremelynarrow area corresponding to the fovea, but is applied to an areacorresponding to the average eye movements, before moving the head. Itmeans that the user can move his gaze around an area with high densityinformation, and enjoy a feeling of immersion thanks to the large fieldof view providing sparse information.

In a HMD device coupled with an inertial measurement unit (IMU), theuser can move his/her head to center of an object or area perceived withlow resolution in periphery, to then dramatically increase theresolution on this object or area.

On a currently available HMD device such as the Oculus Rift HMD, thepixels generated by the display device are distributed by the opticswith an almost constant density over the whole field of view. Since thisoptics is simple, it introduces a strong pincushion distortion that mustbe compensated by signal processing, by applying the inverse deformationto the video content to be displayed. The viewer can perceive a video orgraphic immersive content with a large field of view, but with a poorresolution, even in the central area of the HMD.

What is called “foveation” is known in the technical field of imageacquisition. Images can be acquired thanks to foveated sensors, wherethe density of photosites is higher in the central area of the sensor orwith a standard sensor associated with a foveated lens.

Foveated imaging is also known in the technical field of signalprocessing, covering image compression, image transmission, or gazecontingent displays. For this last application, an eye tracker detectswhere the user is looking, and more information (image portionscontaining high frequencies) is dynamically displayed in this area thanin the periphery (only low frequencies, blur).

It is proposed in this disclosure a system which is configured to (oradapted to) increase the pixel density in an area on the display, anddecreasing the pixel density in the peripheral regions of the area onthe display. However, it should be noted that, unlike foveated imageswhere details (high frequencies) are displayed in the area of interest,and blurry information (or only low frequencies) are displayed inperiphery with a constant pixel density, the proposed system modifiesthe pixel density itself.

The repartition of the pixels may be modified by the transformation Tapplied by the optics. In this case, the content to be displayed needsto be modified by the inverse geometric transformation T⁻¹. Then, anincrease of the pixel density increases the perceived luminance, andvice versa. This modification of luminance needs to be totally orpartially compensated by the display or the signal processing applied tothe images to be displayed.

FIG. 2 presents the general overview according an embodiment of thepresent disclosure.

A conventional optical element modifies the light as if it was generatedat infinity (or at finite but large distance) from the viewer to allowaccommodation by the viewer's eyes. It can also increase the field ofview of the display to improve the feeling of immersion by the viewer.

In addition to the conventional art, the non-limitative embodiment ofthe present disclosure proposes that the optical element applies adistortion (as shown in FIG. 3) to modify the perceived pixel density,depending on the distance to the center. This distance may be radial oraxial, according to the horizontal axes. As can be seen in FIG. 4, thedistortion caused by the optical element of the embodiment of thepresent disclosure provides pixels repartition, that is, constantdensity of pixels displayed on the display is transformed into amodified pixels density in which increased pixels density is perceivedin the central area of field of view.

FIG. 4 illustrates a geometric transformation process applied to animage according to the embodiment of the present disclosure. Beforebeing provided to the display, the input image I is transformed by thefunction T⁻¹(I), preserving the details in the central area. Thistransformation must correspond to the inverse transformation functionapplied by the optical element of the embodiment of the presentdisclosure. It may be approximated for example by a polynomial function.The optical element applies the distortion T(I1), to provide the image Ito the viewer, with a high density of information in the central area(around β) which is the center of the field of view (see FIG. 4).

The pixel density perceived by the viewer is represented by a curve inFIG. 4. The “α” represents the position around β, defining the limitposition where the pixel density is increased or decreased, compared toa constant density of pixels. This curve depends on the opticaltransformation and is given here as an example. The perceived density ofpixels could for instance decrease continuously, up to the maximum fieldof view.

The position β where the perceived density is at a maximum value is hereplaced at ½ FOV (Field of View). This position can vary if the eye movesand be tracked by an eye tracking system on the HMD device. The opticalelement can be shifted left to right, up and down depending on theoutput from the eye tracking system output signal to align the maximumdensity region with the optical axis of a given eye. The image signalwill be modified according to the new T/T⁻¹ transforms associated withthe modified optical configuration. When the eye is tracked and theoptical element shifted accordingly, the value α can be decreased in theoptical design, restricted to the fovea extension but excluding the eyemotion margins considered in the static configuration.

The proposed solution has to be compared to the standard implementationin order to compare the relative perceived pixel density per angularsector.

FIG. 5 illustrates a design of a lens with the same functionality thanin the original system.

The optical system is dimensioned for having a total field of view ofabout 95°, the object field width is 2×37.5 mm, which is the width ofthe screen. FIG. 5 shows the ray tracing for the axial field point, anintermediary one and the marginal field. The system is designed to beafocal in image space and the pupil is of 4 mm at 10 mm distance fromthe sag of the last optical surface. The MTF (Modulation TransferFunction) at the marginal field point is of course pretty bad as thiscan be inferred from the non-collimated red sub-beam reaching the pupil.The perceived field of view in image space is of ±29°.

In order to modify the perceived angular pixel densities, a lens needsto be set up in the vicinity of the object plane. That field lens shallmap the pixels in the central part of the display around the opticalaxis with more angular density in the image space than outer pixels. Theoptical surface with such a property is necessarily an even asphere. Itis a rotationally symmetric polynomial aspheric surface described by apolynomial expansion of the deviation from a spherical surface. The evenasphere surface model uses only the even powers of the radial coordinateto describe the asphericity. The surface sag is given by:

$z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {\alpha_{1}r^{2}} + \ldots + {\alpha_{8}r^{16}}}$

where c is the curvature, r is the radial coordinate in lens units and kis the conic constant. The field lens needs to have both its frontsurface aspheric in order to modulate separately the different locationsof the field points, and it also needs to have a rear aspheric surfacefor pointing each chief ray toward the entrance pupil of the opticalsystem of the HMD device of the present embodiment.

FIG. 6 shows the whole optical system of the HMD device of the presentembodiment, which improves the angular resolution density near the axis.The first lens is the one which is warping the field points to differentangular densities in the image space. Its shape seems complicated but itis made out of B 270 (trademark) glass by SCHOTT AG and can be molded inhigh volumes and low costs as well as the main lens which is also madeof the same material and which also needs to be molded since it also hastwo aspheric surfaces.

The lens prescription is as follows:

Surface Data Summary:

Surf. Type Radius Thickness Glass Diameter Conic Comment OBJ STANDARDInfinity 4.3333 75 0 1 EVENASPH 41.44078 4.669471 BK7 61.37206 0 2EVENASPH 6.699356 40.00001 57.869 2.287118 STO STANDARD Infinity 0 20 04 EVENASPH −22.21413 20 BK7 26.72005 0 5 EVENASPH −18.07581 10 35.417180 IMA STANDARD Infinity 4 0

Surface Data Detail:

Surface OBJ STANDARD Surface 1 EVENASPH Coefficient on r{circumflex over( )} 2 0 Coefficient on r{circumflex over ( )} 4 −6.9859233e−005Coefficient on r{circumflex over ( )} 6 2.4668817e−007 Coefficient onr{circumflex over ( )} 8 −3.9883699e−010 Coefficient on r{circumflexover ( )}10 5.5885882e−013 Coefficient on r{circumflex over ( )}12−6.6854249e−016 Coefficient on r{circumflex over ( )}14 3.6309444e−019Coefficient on r{circumflex over ( )}16 −1.5338173e−023 Surface 2EVENASPH Coefficient on r{circumflex over ( )} 2 0.0028058026Coefficient on r{circumflex over ( )} 4 −2.6206468e−005 Coefficient onr{circumflex over ( )} 6 1.0404351e−008 Coefficient on r{circumflex over( )} 8 1.903396e−011 Coefficient on r{circumflex over ( )}10−6.34717e−015 Coefficient on r{circumflex over ( )}12 0 Coefficient onr{circumflex over ( )}14 0 Coefficient on r{circumflex over ( )}16 0Surface STO STANDARD Surface 4 EVENASPH Coefficient on r{circumflex over( )} 2 0 Coefficient on r{circumflex over ( )} 4 0.00049344985Coefficient on r{circumflex over ( )} 6 1.8727954e−005 Coefficient onr{circumflex over ( )} 8 3.8728936e−007 Coefficient on r{circumflex over( )}10 −4.8665752e−009 Coefficient on r{circumflex over ( )}123.6241717e−011 Coefficient on r{circumflex over ( )}14 −1.4659605e−013Coefficient on r{circumflex over ( )}16 2.4658053e−016 Surface 5EVENASPH Coefficient on r{circumflex over ( )} 2 0 Coefficient onr{circumflex over ( )} 4 0.00019263165 Coefficient on r{circumflex over( )} 6 −4.3484529e−006 Coefficient on r{circumflex over ( )} 85.3643851e−008 Coefficient on r{circumflex over ( )}10 −3.6869579e−010Coefficient on r{circumflex over ( )}12 1.4315606e−012 Coefficient onr{circumflex over ( )}14 −2.9346767e−015 Coefficient on r{circumflexover ( )}16 2.4867346e−018

As a by-side benefit provided by the configuration of the opticalsystem, the MTF has been improved also.

Finally, in order to demonstrate that the optical system shown in FIG. 6has the functionality described in this disclosure, the perceived fieldof view can be plotted as a function of the field position on thedisplay as shown in FIG. 7. As it can be seen from FIG. 7, the improvedsystem has effectively a curve shaped like the theoretical one shown inFIG. 4 resulting in a higher perceived pixel density in the vicinity ofthe optical axis direction.

FIG. 8 schematically illustrates a display device according to anembodiment of the present disclosure, in which FIG. 8(a) is a plan viewof the device and FIG. 8(b) is a front view of the device.

As shown in FIG. 8, a display device 100 may include a display module105 which can be an LCD (Liquid Crystal Display) with a light source oran OLED (Organic Light Emitting Display), for example. Fixing elements110 such as temple arms, that will extend respectively over the ears ofa viewer to help hold the device 100 in place, are mounted on both sidesof the display device 100. Alternatively, the fixing element 110 may bean expansion band to hold the device 100 on viewer's head.

The display device 100 also includes an optical component 120 and anactuator 115 to move the optical component 120. The optical component120 may comprise the two optical elements designed as described above inconnection with FIG. 6. The optical component 120 is connected to theactuator 115 through a connecting member 125. The actuator 115 ismounted on the fixing elements 110 and the optical component 120 issupported by the connecting member 125 in front of the display module105. These actuator 115, optical component 120 and connecting member 125are mounted on both sides of the fixing elements 110, respectively.Thanks to the actuators 115, the optical components 120 can be moved upand down and left to right, as indicated by the arrows shown in FIG.8(b), respectively. It should be noted that each optical element of theoptical component 120 can alternatively have a form of Fresnel lens sothat the optical elements can have thinner shape and lighter weight.

The display device 100 is provided with an eye tracking sensor 130 todetect eye gaze point of the eyes of viewer. The eye tracking sensor 130may be mounted on the upper or lower portion of the display module 105,for example so as to prevent any shading of display screen which may becaused by the sensor 130. Further, display device 100 is provided with aposition sensor 145 such as inertial measurement unit (IMU) to measurethe position of a viewer's head on which the display device 100 ismounted.

The display device 100 further includes a control module 140 to controlthe display module 105, actuators 115, the eye tracking sensor 130 andthe position sensor 145. The control module 140 is connected to theseelements via wired or wireless connection. The control module 140 isalso connected to an external device (not shown) via wired or wirelessconnection. The external device stores images or videos to be providedto the display device 100. The images or videos are provided from theexternal device to the control module 140, then the control module 140presents the received image or video on the display module 105.

The display device 100 may have a hood (not shown) surrounding theperiphery of the display module 105 to provide a dark space in the fieldof view of the viewer, which may provide the viewer with better feelingof immersion.

FIG. 9 is a block diagram illustrating components of the control moduleshown in FIG. 8.

As shown in FIG. 9, the control module 200 comprises an I/O interface210 and a memory device 220. The interface 210 and memory device 220 areconfigured to receive and store images or videos to be presented on thedisplay module 105 (FIG. 8).

The module 200 further comprises a processor 230. The processor 230performs to detect eye gaze point of the viewer based on the inputs fromthe eye tracking sensor 130, to activate the actuators 115 in responseto the detected eye gaze point, to present images or videos receivedfrom the external device on the display module 105 and to scroll theimages or videos displayed on the display module 105 in response to aviewer's head position detected and input by the position sensor 145.

The processor 230 further performs to modify the images or videos byapplying a geometric transformation T⁻¹(I) as described in reference toFIG. 4 so that information density of the images or videos in an areaaround the detected eye gaze point on the display 105 (FIG. 8) can beincreased. The processor 230 may further apply luminance compensation tocompensate a variation of luminance in the images or videos which couldbe caused by the geometric transformation T⁻¹(I). The memory device 220is also configured to store at least one program to be executed by theprocessor 230 for performing the above mentioned processes.

FIG. 10 is a flow chart illustrating an example of a process performedby the display device according to an embodiment of the presentdisclosure.

At step S10, the control module 140; 200 of the display device 100receives an immersive, image or video content from an external device(not shown) via its I/O interface 210. The received content is stored onthe memory module 230. The immersive content may be a whole contentavailable for the HMD device to display a 360° content (or less than360°, but more than what can be displayed by the HMD's display screen),in other words, the immersive content may have wider area than the areaof HMD's display screen. Thanks to such an immersive content, a viewercan be immersed in a virtual world displayed on the HMD device and canmove his/her head to select a part of the whole 360° content he/shewants to see.

At step S12, the viewer's head position is detected by the positionsensor 145, then at step S14, a part of the 360° content to be displayedon the HMD device is selected by the processor 220. The part of the 360°content that the viewer wants to see corresponds to the detected headposition.

At step S16, eye gaze position of the eyes of viewer on which thedisplay device 100 is mounted is determined by the eye tracking sensor130. The detected information is output from the sensor 130 to theprocessor 220 of the control module 200. Based on the detectedinformation, the processor 220 performs an analysis for specifying aneye gaze position of the eyes of viewer on the display module 105, inother words, for specifying which area on the display module 105 theviewer is watching. It should be noted that the step S16 can beperformed during steps S10-S14.

Alternatively, at step S16, information of Region of Interest (ROI) inthe content can be employed to determine eye gaze position of the eyesof viewer instead of the detection of eye gaze position by the eyetracking sensor 130. In this case, areas of ROI in the content (eachimage or each frame of video) can be determined in advance by test usersor by any known dedicated ROI analysis software and associated with thecontent via metadata incorporated in the content. The areas of ROI inthe content can be presumed eye gaze positions since the viewer mostlikely pay attention to the area of ROI in the content and thus eye gazewill be even more attracted by these ROIs.

At step S18, the processor 220 reads out the image or video stored inthe memory module 230 and modifies the image or video so that an areahaving higher density information of the image or video can be formed atthe specified eye gaze position on the display 105. The modification ofthe image or video may be performed by applying a geometrictransformation which corresponds to the inverse transformation functionapplied by the optical components 120 (FIG. 4). Then, the processor 220presents the modified image or video content on the display device 105.

At step S20, the processor 220 controls the actuators 115 to move therespective optical components 120 in response to the specified eye gazeposition on the display 105 so that the viewer can see the display 105through the optical components 120. For example, an association betweeneye gazes positions on the display 105 and their respectivecorresponding positions of the optical components 120 may be establishedin advance and stored on the memory module 230. In this case, theprocessor 220 causes the actuators 115 to move the optical components120 to a position which corresponds to the detected eye gaze positionaccording to the association.

Since the optical components 120 apply the distortion T(I1) which willcompensate the transformation made on the image or video presented onthe display 105, the image or video content perceived by the viewerthrough the optical components 120 has a higher density of informationin the eye gaze position than that in the periphery of the eye gazeposition.

The steps S12 through S20 may be repeated during the image or videocontent is presented on the display 105, which allows to change thedense information area on the image or video (the area of the image orvideo content having higher density of information than that in the restof the content) and the positions of the optical components 120 inresponse to the detected eye gaze position in real time.

According the embodiment, the density of information available in theeye gaze area on the display 105 can be dramatically increased, thusmore details can be provided in this area. On the other hand, since thevisual acuity is much lower in peripheral vision, the feeling ofimmersion brought by a large field of view can be preserved.

Alternatively, the dense information area on the image or video and thepositions of the optical components 120 may be fixed, for example, thedense information area on the image or video may be fixed in the centralarea of the image or video on the display 105 and positions of opticalcomponents 120 may be the corresponding positions. In this case, theabove described steps S12 and S16 may be omitted.

Yet alternatively, at step S14, the processor 220 may modify the imageor video directly received from the external device and present themodified image or video on the display device 105. In this case, thereceived image or video content may not be stored on the memory module230.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the disclosure.

1. A method for presenting an image on a display device, including:modifying the image by applying a geometric transformation to the imageso that an area of the image on the display device is presented to aviewer with higher density of pixels than that in the rest of the image.2. The method according to claim 1, wherein the method further includingpresenting the image on the display device to the viewer through anoptical component applying an inverse transformation corresponding tothe geometric transformation that has been applied to the image.
 3. Themethod according to claim 2, wherein the method further including:determining eye gaze position of the viewer; and changing the area ofthe image on the display device having the higher density of pixels andthe position of the optical component in response to the determined eyegaze position.
 4. The method according to claim 1, wherein the positionof the area of the image on the display device having the higher densityof pixels is fixed at a predetermined position on the display device. 5.The method according to claim 1, wherein the display device is a headmounted display (HMD) device.
 6. The method according to claim 5,wherein the content has wider area than what can be displayed on thedisplay device, and wherein the method further including: detecting ahead position of the viewer; and selecting a part of the image to bedisplayed on the display device in response to the detected headposition.
 7. A display device for presenting an image comprising atleast a processor configured to: modify the image by applying ageometric transformation to the image so that an area of the image onthe display device is presented to a viewer with higher density ofpixels than that in the rest of the image.
 8. The display deviceaccording to claim 7, wherein the display device further comprising anoptical component through which the image on the display device ispresented to the viewer, wherein the optical component is configured toapply an inverse transformation corresponding to the geometrictransformation that has been applied to the image.
 9. The display deviceaccording to claim 8, wherein the display device further comprising aneye tracking sensor, and wherein the processor is further configured to:determine eye gaze position of the viewer in cooperation with the eyetracking sensor; and change the area of the image on the display devicehaving the higher density of pixels and the position of the opticalcomponent in response to the determined eye gaze position.
 10. Thedisplay device according to claim 8, wherein the processor is furtherconfigured to: determine eye gaze position of the viewer based oninformation of Region of Interests incorporated in the content; andchange the area of the image on the display device having the higherdensity of pixels and the position of the optical component in responseto the determined eye gaze position.
 11. The display device according toclaim 9, wherein the display device further comprising an actuator tomove the optical component, the position of the optical component ischanged by operating the actuator in response to the determined eye gazeposition.
 12. The display device according to claim 7, wherein theposition of the area of the image on the display device having thehigher density of pixels is fixed at a predetermined position on thedisplay device.
 13. The display device according to claim 7, wherein thedisplay device is a head mounted display (HMD) device.
 14. The displaydevice according to claim 13, wherein the display device furthercomprising a position sensor to detect a head position of the viewer,wherein the image has wider area than what can be displayed on thedisplay device, and wherein the processor is further configured to:detect a head position of the viewer in cooperation with the positionsensor; and select a part of the image to be displayed on the displaydevice in response to the detected head position.